U.S. patent application number 15/658464 was filed with the patent office on 2019-01-31 for low emissions combustor assembly for gas turbine engine.
The applicant listed for this patent is United Technologies Corporation. Invention is credited to Jeffrey M. Cohen, Zhongtao Dai, Lance L. Smith.
Application Number | 20190032559 15/658464 |
Document ID | / |
Family ID | 63047239 |
Filed Date | 2019-01-31 |
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United States Patent
Application |
20190032559 |
Kind Code |
A1 |
Dai; Zhongtao ; et
al. |
January 31, 2019 |
LOW EMISSIONS COMBUSTOR ASSEMBLY FOR GAS TURBINE ENGINE
Abstract
A combustor assembly for a gas turbine engine according to an
example of the present disclosure includes, among other things, a
combustion chamber, and a fuel injector assembly in communication
with the combustion chamber that has a swirler body situated about
a nozzle to define an injector passage that converges to a throat.
The throat is defined at a distance from the combustion chamber.
The nozzle includes a primary fuel injector along a first fuel
injector axis and at least one secondary plain jet fuel injector
axially forward of the primary fuel injector.
Inventors: |
Dai; Zhongtao; (West
Hartford, CT) ; Smith; Lance L.; (West Hartford,
CT) ; Cohen; Jeffrey M.; (Hebron, CT) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
United Technologies Corporation |
Farmington |
CT |
US |
|
|
Family ID: |
63047239 |
Appl. No.: |
15/658464 |
Filed: |
July 25, 2017 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
F05D 2220/32 20130101;
F23D 2900/00015 20130101; F23R 3/14 20130101; F23R 3/26 20130101;
F23D 2202/00 20130101; F23D 11/383 20130101; F23R 3/343 20130101;
F02C 3/04 20130101; F02C 9/26 20130101; F23R 3/346 20130101; F23R
2900/03343 20130101; Y02T 50/60 20130101; F23D 2900/00008 20130101;
F23R 3/286 20130101; F23R 3/28 20130101; F02C 7/222 20130101; F02K
3/06 20130101; F05D 2220/323 20130101; F23C 7/004 20130101; F23D
2900/11001 20130101 |
International
Class: |
F02C 7/22 20060101
F02C007/22; F02C 3/04 20060101 F02C003/04; F02C 9/26 20060101
F02C009/26; F23R 3/26 20060101 F23R003/26; F23R 3/28 20060101
F23R003/28 |
Goverment Interests
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
[0001] This invention was made with government support under
Contract No. NNC14CA30C, awarded by the United States National
Aeronautics and Space Administration (NASA). The Government has
certain rights in this invention.
Claims
1. A combustor assembly for a gas turbine engine comprising: a
combustion chamber; a fuel injector assembly in communication with
the combustion chamber, comprising: a swirler body situated about a
nozzle to define an injector passage that converges to a throat,
the throat defined at a distance from the combustion chamber; and
wherein the nozzle includes a primary fuel injector along a first
fuel injector axis and at least one secondary plain jet fuel
injector axially forward of the primary fuel injector.
2. The combustor assembly as recited in claim 1, wherein the
injector passage includes a first passage section merging into a
second passage section, the first passage section defined between
the swirler body and the nozzle, and the second passage section
defining the throat.
3. The combustor assembly as recited in claim 2, wherein a radially
outer wall of the first passage section slopes toward the first
fuel injector axis to define a first passage angle, the first
passage angle being between about 30 degrees and about 50
degrees.
4. The combustor assembly as recited in claim 3, wherein a radially
inner wall of the first passage section slopes toward the first
fuel injector axis to define a second passage angle, the second
passage angle being within about 5 degrees of the first passage
angle.
5. The combustor assembly as recited in claim 1, wherein the
injector passage defines a first passage area with respect to a
first reference plane that is perpendicular to the first fuel
injector axis and intersects an outlet of the at least one
secondary plain-jet fuel injector, the injector passage defines a
second passage area with respect to a second reference plane along
the throat that is perpendicular to the first fuel injector axis,
and a ratio of the first passage area to the second passage area
being about 1.2 to about 1.5.
6. The combustor assembly as recited in claim 5, wherein the
injector passage diverges aft of the throat with respect to the
first fuel injector axis.
7. The combustor assembly as recited in claim 1, wherein an outlet
of the at least one secondary plain-jet fuel injector and the
throat define a first distance with respect to the first fuel
injector axis, an outlet of the primary fuel injector and the
throat defines a second distance with respect to the first fuel
injector axis, and a ratio of the first distance to the second
distance being between about 2.0 to about 4.0.
8. The combustor assembly as recited in claim 7, wherein the at
least one secondary plain jet defines a second fuel injector axis,
the at least one secondary plain-jet fuel injector arranged such
that a projection of the second fuel injector axis intersects an
outer wall of the injector passage.
9. The combustor assembly as recited in claim 1, wherein the
primary fuel injector is arranged to generate a non-premixed fuel
stream, and the at least one secondary plain-jet fuel injector is
arranged to generate a substantially premixed fuel stream.
10. The combustor assembly as recited in claim 9, comprising a
control that meters flow of fuel to the primary fuel injector and
flow of fuel to the at least one secondary plain-jet fuel injector
in a first mode, and meters flow of fuel to the primary fuel
injector and to the at least one secondary plain-jet fuel injector
in a second, different mode such that a rate of the flow of fuel to
the primary fuel injector and the at least one secondary plain-jet
fuel injector differs from the first mode.
11. A gas turbine engine comprising: a fan section including a
plurality of fan blades rotatable about an engine axis; a
compressor section in fluid communication with the fan section; a
turbine section driving the fan section; and a combustor section in
fluid communication with the compressor section and the turbine
section, the combustor section comprising: a combustion chamber
extending from a bulkhead; a fuel injector assembly along the
bulkhead, the fuel injector assembly including a nozzle extending
along a nozzle axis and a swirler body, the nozzle including a
primary fuel injector along the nozzle axis and an array of
secondary plain-jet fuel injectors arranged about a periphery of
the nozzle, and the swirler body situated about the nozzle to
define an injector passage that converges to a throat such that
flow through the injector passage accelerates towards the
throat.
12. The gas turbine engine as recited in claim 11, wherein the
throat is defined at a position axially forward of the combustion
chamber relative to the nozzle axis.
13. The gas turbine engine as recited in claim 12, wherein the
injector passage includes a first passage section merging into a
second passage section, the first passage section being an annulus
defined between the swirler body and the nozzle, the first passage
section extending from an array of vanes that provide airflow to
the first passage section, and the second passage section defining
the throat at a position axially aft of the primary fuel injector
relative to the nozzle axis.
14. The gas turbine engine as recited in claim 11, comprising a
controller that meters flow of fuel to the primary fuel injector
and flow of fuel to the array of secondary plain-jet fuel injector
in a first operating condition of the engine, and meters flow of
fuel to the primary fuel injector and to the array of secondary
plain-jet fuel injectors in a second, different operating condition
of the engine such that a rate of the flow of fuel to the primary
fuel injector and the array of secondary plain-jet fuel injectors
differs from the first operating condition.
15. The gas turbine engine as recited in claim 14, comprising a
main fuel injector radially disposed about the combustion chamber
at a location axially aft of the bulkhead, wherein the controller
permits flow to the main fuel injector in the second operating
condition but not the first operating condition, wherein the first
operating condition is a low power operating condition of the
engine, and the second operating condition is a relatively higher
power operating condition of the engine.
16. A method of operating a combustor assembly for a gas turbine
engine comprising: accelerating airflow in an injector passage from
a first passage section toward a throat defined by a second passage
section; injecting fuel into the first passage section and fuel
into the second passage section to establish a single non-premixed
flame during a first, different mode; and injecting fuel into the
first passage section to establish a non-premixed flame and fuel
into the second passage section to establish a premixed flame
during a second mode.
17. The method as recited in claim 16, comprising injecting fuel
into a combustion chamber at a location downstream of the injector
passage to establish a main flame during the second mode, but not
the first mode.
18. The method as recited in claim 16, wherein the first mode
corresponds to low power operating condition of the engine, and the
second mode corresponds to higher power operating condition of the
engine.
19. The method as recited in claim 16, wherein the first passage
section defines a first passage area, the second passage section
defines a second passage area at the throat, and a ratio of the
first passage area to the second passage area being about 1.2 to
about 1.5.
20. The method as recited in claim 19, wherein the second passage
section diverges between the throat and a combustion chamber, the
combustion chamber at a location downstream of the injector
passage.
Description
BACKGROUND
[0002] This application relates to combustor arrangements for a gas
turbine engine, including combustors having low nitrogen oxide
(NOx) and soot emissions.
[0003] Gas turbine engines are known, and typically include a fan
delivering air into a low pressure compressor section. The air is
compressed in the low pressure compressor section, and passed into
a high pressure compressor section. From the high pressure
compressor section the air is introduced into a combustor section
where it is mixed with fuel and ignited. Products of this
combustion pass downstream over a high pressure turbine section,
and then a low pressure turbine section to extract energy for
driving the fan.
[0004] Some combustor sections have a pilot injector and a main
injector that introduce fuel into a combustion chamber where the
fuel is burned. The pilot injector typically causes a relatively
hot, stable, non-premixed-type pilot flame to be produced for
igniting a fuel stream injected into the combustion chamber by the
main injector to produce a main flame. The non-premixed flame can
be associated with relatively high NOx emissions and levels of
soot.
SUMMARY
[0005] A combustor assembly for a gas turbine engine according to
an example of the present disclosure includes a combustion chamber,
and a fuel injector assembly in communication with the combustion
chamber that has a swirler body situated about a nozzle to define
an injector passage that converges to a throat. The throat is
defined at a distance from the combustion chamber. The nozzle
includes a primary fuel injector along a first fuel injector axis
and at least one secondary plain jet fuel injector axially forward
of the primary fuel injector.
[0006] In a further embodiment of any of the foregoing embodiments,
the injector passage includes a first passage section merging into
a second passage section. The first passage section is defined
between the swirler body and the nozzle, and the second passage
section defines the throat.
[0007] In a further embodiment of any of the foregoing embodiments,
a radially outer wall of the first passage section slopes toward
the first fuel injector axis to define a first passage angle. The
first passage angle is between about 30 degrees and about 50
degrees.
[0008] In a further embodiment of any of the foregoing embodiments,
a radially inner wall of the first passage section slopes toward
the first fuel injector axis to define a second passage angle. The
second passage angle is within about 5 degrees of the first passage
angle.
[0009] In a further embodiment of any of the foregoing embodiments,
the injector passage defines a first passage area with respect to a
first reference plane that is perpendicular to the first fuel
injector axis and intersects an outlet of the at least one
secondary plain-jet fuel injector. The injector passage defines a
second passage area with respect to a second reference plane along
the throat that is perpendicular to the first fuel injector axis,
and a ratio of the first passage area to the second passage area
being about 1.2 to about 1.5.
[0010] In a further embodiment of any of the foregoing embodiments,
the injector passage diverges aft of the throat with respect to the
first fuel injector axis.
[0011] In a further embodiment of any of the foregoing embodiments,
an outlet of the at least one secondary plain-jet fuel injector and
the throat define a first distance with respect to the first fuel
injector axis, an outlet of the primary fuel injector and the
throat defines a second distance with respect to the first fuel
injector axis, and a ratio of the first distance to the second
distance being between about 2.0 to about 4.0.
[0012] In a further embodiment of any of the foregoing embodiments,
the at least one secondary plain jet defines a second fuel injector
axis. The at least one secondary plain-jet fuel injector is
arranged such that a projection of the second fuel injector axis
intersects an outer wall of the injector passage.
[0013] In a further embodiment of any of the foregoing embodiments,
the primary fuel injector is arranged to generate a non-premixed
fuel stream, and the at least one secondary plain-jet fuel injector
is arranged to generate a substantially premixed fuel stream.
[0014] A further embodiment of any of the foregoing embodiments
includes a control that meters flow of fuel to the primary fuel
injector and flow of fuel to the at least one secondary plain-jet
fuel injector in a first mode, and meters flow of fuel to the
primary fuel injector and to the at least one secondary plain-jet
fuel injector in a second, different mode such that a rate of the
flow of fuel to the primary fuel injector and the at least one
secondary plain-jet fuel injector differs from the first mode.
[0015] A gas turbine engine according to an example of the present
disclosure includes a fan section that has a plurality of fan
blades rotatable about an engine axis, a compressor section in
fluid communication with the fan section, a turbine section that
drives the fan section, and a combustor section in fluid
communication with the compressor section and the turbine section.
The combustor section has a combustion chamber that extends from a
bulkhead, and a fuel injector assembly along the bulkhead. The fuel
injector assembly has a nozzle that extends along a nozzle axis and
a swirler body. The nozzle has a primary fuel injector along the
nozzle axis and an array of secondary plain-jet fuel injectors
arranged about a periphery of the nozzle. The swirler body is
situated about the nozzle to define an injector passage that
converges to a throat such that flow through the injector passage
accelerates towards the throat.
[0016] In a further embodiment of any of the foregoing embodiments,
the throat is defined at a position axially forward of the
combustion chamber relative to the nozzle axis.
[0017] In a further embodiment of any of the foregoing embodiments,
the injector passage includes a first passage section merging into
a second passage section. The first passage section is an annulus
defined between the swirler body and the nozzle. The first passage
section extends from an array of vanes that provide airflow to the
first passage section, and the second passage section defines the
throat at a position axially aft of the primary fuel injector
relative to the nozzle axis.
[0018] A further embodiment of any of the foregoing embodiments
includes a controller that meters flow of fuel to the primary fuel
injector and flow of fuel to the array of secondary plain-jet fuel
injector in a first operating condition of the engine, and meters
flow of fuel to the primary fuel injector and to the array of
secondary plain-jet fuel injectors in a second, different operating
condition of the engine such that a rate of the flow of fuel to the
primary fuel injector and the array of secondary plain-jet fuel
injectors differs from the first operating condition.
[0019] A further embodiment of any of the foregoing embodiments
includes a main fuel injector radially disposed about the
combustion chamber at a location axially aft of the bulkhead. The
controller permits flow to the main fuel injector in the second
operating condition but not the first operating condition. The
first operating condition is a low power operating condition of the
engine, and the second operating condition is a relatively higher
power operating condition of the engine.
[0020] A method of operating a combustor assembly for a gas turbine
engine according to an example of the present disclosure includes
accelerating airflow in an injector passage from a first passage
section toward a throat defined by a second passage section,
injecting fuel into the first passage section and fuel into the
second passage section to establish a single non-premixed flame
during a first, different mode, and injecting fuel into the first
passage section to establish a non-premixed flame and fuel into the
second passage section to establish a premixed flame during a
second mode.
[0021] A further embodiment of any of the foregoing embodiments
includes injecting fuel into a combustion chamber at a location
downstream of the injector passage to establish a main flame during
the second mode, but not the first mode.
[0022] In a further embodiment of any of the foregoing embodiments,
the first mode corresponds to low power operating condition of the
engine, and the second mode corresponds to higher power operating
condition of the engine.
[0023] In a further embodiment of any of the foregoing embodiments,
the first passage section defines a first passage area. The second
passage section defines a second passage area at the throat, and a
ratio of the first passage area to the second passage area being
about 1.2 to about 1.5.
[0024] In a further embodiment of any of the foregoing embodiments,
the second passage section diverges between the throat and a
combustion chamber at a location downstream of the injector
passage.
[0025] The details of one or more embodiments are set forth in the
accompanying drawings and the description below. Other features,
objects, and advantages will be apparent from the description and
drawings, and from the claims.
BRIEF DESCRIPTION OF THE DRAWINGS
[0026] FIG. 1 illustrates a gas turbine engine.
[0027] FIG. 2 illustrates a perspective view of an example
combustor assembly.
[0028] FIG. 3 illustrates a perspective view of an example pilot
fuel injector assembly that can be utilized with the combustor
assembly of FIG. 2.
[0029] FIG. 4 illustrates a cross-sectional view of the pilot fuel
injector assembly of FIG. 3.
[0030] FIG. 5 shows a cross-sectional view of selected portions of
the pilot fuel injector assembly of FIG. 4 illustrating various
dimensional relationships.
[0031] FIG. 6 illustrates a cross-sectional view of selected
portions of the pilot fuel injector assembly of FIG. 4 illustrating
other various dimensional relationships.
[0032] FIG. 7 illustrates a process for operating a combustor
assembly.
[0033] FIG. 8 illustrates various flame geometries associated with
the combustor assembly of FIG. 2.
[0034] Like reference numbers and designations in the various
drawings indicate like elements.
DETAILED DESCRIPTION
[0035] FIG. 1 schematically illustrates a gas turbine engine 20.
The gas turbine engine 20 is disclosed herein as a two-spool
turbofan that generally incorporates a fan section 22, a compressor
section 24, a combustor section 26 and a turbine section 28.
Alternative engines might include an augmentor section (not shown)
among other systems or features. The fan section 22 drives air
along a bypass flow path B in a bypass duct defined within a
nacelle 15, and also drives air along a core flow path C for
compression and communication into the combustor section 26 then
expansion through the turbine section 28. Although depicted as a
two-spool turbofan gas turbine engine in the disclosed non-limiting
embodiment, it should be understood that the concepts described
herein are not limited to use with two-spool turbofans as the
teachings may be applied to other types of turbine engines
including three-spool architectures.
[0036] The exemplary engine 20 generally includes a low speed spool
30 and a high speed spool 32 mounted for rotation about an engine
central longitudinal axis A relative to an engine static structure
36 via several bearing systems 38. It should be understood that
various bearing systems 38 at various locations may alternatively
or additionally be provided, and the location of bearing systems 38
may be varied as appropriate to the application.
[0037] The low speed spool 30 generally includes an inner shaft 40
that interconnects a fan 42, a first (or low) pressure compressor
44 and a first (or low) pressure turbine 46. The inner shaft 40 is
connected to the fan 42 through a speed change mechanism, which in
exemplary gas turbine engine 20 is illustrated as a geared
architecture 48 to drive the fan 42 at a lower speed than the low
speed spool 30. The high speed spool 32 includes an outer shaft 50
that interconnects a second (or high) pressure compressor 52 and a
second (or high) pressure turbine 54. A combustor 56 is arranged in
exemplary gas turbine 20 between the high pressure compressor 52
and the high pressure turbine 54. A mid-turbine frame 57 of the
engine static structure 36 is arranged generally between the high
pressure turbine 54 and the low pressure turbine 46. The
mid-turbine frame 57 further supports bearing systems 38 in the
turbine section 28. The inner shaft 40 and the outer shaft 50 are
concentric and rotate via bearing systems 38 about the engine
central longitudinal axis A which is collinear with their
longitudinal axes.
[0038] The core airflow is compressed by the low pressure
compressor 44 then the high pressure compressor 52, mixed and
burned with fuel in the combustor 56, then expanded over the high
pressure turbine 54 and low pressure turbine 46. The mid-turbine
frame 57 includes airfoils 59 which are in the core airflow path C.
The turbines 46, 54 rotationally drive the respective low speed
spool 30 and high speed spool 32 in response to the expansion. It
will be appreciated that each of the positions of the fan section
22, compressor section 24, combustor section 26, turbine section
28, and fan drive gear system 48 may be varied. For example, gear
system 48 may be located aft of combustor section 26 or even aft of
turbine section 28, and fan section 22 may be positioned forward or
aft of the location of gear system 48.
[0039] The engine 20 in one example is a high-bypass geared
aircraft engine. In a further example, the engine 20 bypass ratio
is greater than about six (6), with an example embodiment being
greater than about ten (10), the geared architecture 48 is an
epicyclic gear train, such as a planetary gear system or other gear
system, with a gear reduction ratio of greater than about 2.3 and
the low pressure turbine 46 has a pressure ratio that is greater
than about five. In one disclosed embodiment, the engine 20 bypass
ratio is greater than about ten (10:1), the fan diameter is
significantly larger than that of the low pressure compressor 44,
and the low pressure turbine 46 has a pressure ratio that is
greater than about five 5:1. Low pressure turbine 46 pressure ratio
is pressure measured prior to inlet of low pressure turbine 46 as
related to the pressure at the outlet of the low pressure turbine
46 prior to an exhaust nozzle. The geared architecture 48 may be an
epicycle gear train, such as a planetary gear system or other gear
system, with a gear reduction ratio of greater than about 2.3:1. It
should be understood, however, that the above parameters are only
exemplary of one embodiment of a geared architecture engine and
that the present invention is applicable to other gas turbine
engines including direct drive turbofans.
[0040] A significant amount of thrust is provided by the bypass
flow B due to the high bypass ratio. The fan section 22 of the
engine 20 is designed for a particular flight condition--typically
cruise at about 0.8 Mach and about 35,000 feet (10,668 meters). The
flight condition of 0.8 Mach and 35,000 ft (10,668 meters), with
the engine at its best fuel consumption--also known as "bucket
cruise Thrust Specific Fuel Consumption (`TSFC`)"--is the industry
standard parameter of lbm of fuel being burned divided by lbf of
thrust the engine produces at that minimum point. "Low fan pressure
ratio" is the pressure ratio across the fan blade alone, without a
Fan Exit Guide Vane ("FEGV") system. The low fan pressure ratio as
disclosed herein according to one non-limiting embodiment is less
than about 1.45. "Low corrected fan tip speed" is the actual fan
tip speed in ft/sec divided by an industry standard temperature
correction of [(Tram .degree. R)/(518.7.degree. R)].sup.0.5. The
"Low corrected fan tip speed" as disclosed herein according to one
non-limiting embodiment is less than about 1150 ft/second (350.5
meters/second).
[0041] FIG. 2 illustrates a cross-sectional view of a combustor
assembly 60 for combustion of fuel within a combustion chamber 62.
The combustor assembly 60 can be utilized in the combustor 56 of
engine 20, with products of combustion delivered to the turbine
section 28, for example. Although the combustor assembly 60 is
primarily discussed with respect to a turbofan gas turbine engine
such as engine 20, other systems may also benefit from the
teachings herein, including land-based and marine-based gas turbine
engines.
[0042] The combustor assembly 60 includes a housing 61 supporting
one or more radially outer (or first) panels 62A and one or more
radially inner (or second) panels 62B. The panels 62A, 62B extend
in an aft direction from a generally radially extending bulkhead
62C with respect to a combustor cross sectional centerline axis X
to define the combustion chamber 62. The combustor axis X can be
substantially co-linear with, or transverse to, the engine
longitudinal axis A (FIG. 1). The panels 62A, 62B and bulkhead 62C
can include liners that substantially thermally isolate the
combustion chamber 62 from a chamber 65 and other adjacent portions
of the combustor 56 (FIG. 1). The chamber 65 can receive
pressurized, relatively cool airflow from an upstream portion of
the engine 20, for example, that can be utilized in the combustion
process.
[0043] The combustor 56 can include a plurality of combustor
assemblies 60 disposed in an array about the combustor axis X, each
associated with a respective combustion chamber 62 that can have a
substantially cylindrical profile, for example. In other examples,
the combustion chamber 62 is an annulus swept about the combustor
axis X and is in fluid communication with an array of combustor
assemblies 60 circumferentially distributed about the combustor
axis X.
[0044] The combustor assembly 60 can include one or more main fuel
injector assemblies 64 in communication with a main zone MZ of the
combustion chamber 62 and one or more pilot fuel injector
assemblies 70 in communication with a pilot zone PZ of the
combustion chamber 62 generally upstream of the main zone MZ. The
main fuel injector assembly 64 can be operable to cause a main,
substantially premixed flame to be produced for relatively high
power conditions, and the pilot fuel injector assembly 70 can be
operable to cause a pilot flame to be produced to provide energy
during relatively low power conditions, and ignition and stability
of the main flame during high power operations. Example high power
(or second) conditions may include a late acceleration, takeoff,
climb or cruise operating condition of the engine 20. Example low
power (or first) conditions may include ground idle, idle
(taxiing), initial acceleration, flight idle and approach operating
condition of the engine 20. The pilot flame can be relatively
smaller during high power conditions as compared to low power
conditions of the engine 20, taking less than 25% of total fuel,
for example.
[0045] The main fuel injector assembly 64 can be coupled to a main
fuel line 68, which may be metered by a main valve 66. The main
valve 66 can be coupled to a fuel source FS. The main valve 66 can
be coupled to a control CTRL operable to modulate the main valve 66
to deliver a desired amount of fuel from the fuel source FS through
the main fuel line 68 during different operating modes of the
combustion assembly 60 or operating conditions of the engine
20.
[0046] The main fuel injector assembly 64 can include one or more
injectors which cause fuel from the main fuel line 68 to be
injected into the combustion chamber 62 in a generally radial
direction to cause a main flame to be generated. The main fuel
injector assembly 64 can include a mixer that substantially mixes
fuel from the main fuel line 68 with air to produce a premixed
flame in the combustion chamber 62. The premixed flame may
correspond to a flame having relatively low NOx and soot emissions.
For the purposes of this disclosure, the term "premixed" refers to
a fuel/air mixture stream comprising fuel and air that is
substantially mixed prior to being burned, and the term
"non-premixed" refers to fuel which is mixed with air while being
burned.
[0047] Referring to FIGS. 3 and 4, with continued reference to FIG.
2, the pilot fuel injector assembly 70 includes a housing or
swirler body 72 that is disposed about a nozzle 74, with the
housing or swirler body 72 and the nozzle 74 being distinct and
separable components. In alternative examples, the nozzle 74 and at
least portions of the housing or swirler body 72 are integrally
formed. The swirler body 72 can be situated relative to an opening
or aperture 63 defined by the bulkhead 62C, with the swirler body
72 and the bulkhead 62C being distinct and separable components. In
alternative examples, the bulkhead 62C and at least portions of the
swirler body 72 are integrally formed. The swirler body 72 extends
between a first end portion 72A and a second end portion 72B. The
first end portion 72A extends about at least a portion of the
nozzle 74. The second end portion 72B can extend aftwards through
at least a portion of the bulkhead 62C and into the combustion
chamber 62.
[0048] The nozzle 74 includes a nozzle body 74A that extends along
a nozzle longitudinal axis N between a first end portion 74B and a
second end portion 74C. The nozzle longitudinal axis N can be
substantially parallel to the combustor axis X, for example, and
the combustor axis X can be parallel or have an angle (pitch angle)
to the engine axis A. The nozzle body 74A can have a generally
cylindrical profile, for example, with the nozzle body 74A tapering
at the second end portion 74C to have a substantially rounded or
dome shaped profile.
[0049] The nozzle 74 is situated relative to the swirler body 72 to
define a first (or radially inner) injector passage 88 for
delivering airflow and fuel downstream toward the combustion
chamber 62. The swirler body 72 can define a second (or radially
outer) injector passage 89 radially disposed about at least a
portion of the first injector passage 88 for delivering airflow to
the combustion chamber 62. Each of the injector passages 88, 89
receive airflow from the chamber 65 which can vary during different
operating conditions or engine cycles of the engine 20 (e.g.,
decrease during low power conditions and increase during high power
conditions).
[0050] The second injector passage 89 can be in the shape of an
annulus that tapers in the aft direction, for example. In some
examples, between about 50-95 percent of the total airflow to the
pilot fuel injector assembly 70 is communicated to the first
injector passage 88 at a relatively lower swirl number, and between
about 5-50 percent of the total airflow is communicated to the
second injector passage 89 at a relatively higher swirl number. In
one example, about 85 percent of the airflow is delivered by the
first injector passage 88, and about 15 percent of the total
airflow is delivered by the second injector passage 89. Airflow
from the second injector passage 89 can be directed toward the
radially-most corners of the combustion chamber 62 adjacent the
bulkhead 62C to improve the combustion process.
[0051] The pilot fuel injector assembly 70 includes at least one
primary fuel injector 76 and one or more secondary fuel injectors
78. In one example, the pilot fuel injector assembly 70 includes
one primary pressure swirl fuel injector 76 and an array of six
secondary plain-jet fuel injectors 78 arranged about a periphery of
the nozzle 74. The primary fuel injector 76 extends along a first
fuel injector axis F1 that can be collinear with the nozzle
longitudinal axis N of the nozzle 74 such that the primary fuel
injector 76 is situated at a terminal end of the second end portion
74C of the nozzle 74. In other examples, the first fuel injector
axis F1 is offset from, or transverse to, the nozzle longitudinal
axis N. In the illustrated example, the primary fuel injector 76
ejects a primary (or first) fuel stream S1 (FIG. 4) toward the
combustion chamber 62 in a generally cone shape having an axis of
the cone along the nozzle longitudinal axis N. The primary fuel
stream S1 cone angle is generally the same as an exit angle (i.e.,
prefilmer angle) of outlet 76B of primary fuel injector 76 for
improving fuel atomization and distribution in the non-pre-mixed
pilot flame.
[0052] The primary fuel injector 76 can be a fluid communication
with a primary fuel line 80, and each secondary plain-jet fuel
injectors 78 can be coupled to a secondary fuel line 82 (FIG. 2).
The primary fuel line 80 can be coupled to primary valve 84, and
the secondary fuel line 82 can be coupled to a secondary valve 86
(FIG. 2). The valves 84, 86 can be coupled to control CTRL (FIG.
2), which can be configured to cause fuel source FS (FIG. 2) to
deliver a desired amount of fuel to the respective fuel injectors
76, 78. In the illustrated example, the primary fuel line 80
delivers fuel to the primary fuel injector 76, and the secondary
fuel line 82 delivers fuel to the secondary plain-jet fuel
injectors 78. In some examples, the fuel split between primary and
secondary fuel lines 80, 82 of the pilot injector are
pre-determined for all power operations based on the total pilot
injector assembly 70 fuel flow rate or fuel pressure to reduce the
complexity of combustor fuel control system.
[0053] Referring to FIG. 4, the primary fuel injector 76 includes a
passage 76A that receives fuel from the primary fuel line 80 (FIG.
2) for injection through an outlet 76B. The outlet 76B can be
coupled to a spin chamber or swirler 76C for improving the
atomization quality of non-premixed fuel from the passage 76A. Each
secondary plain-jet fuel injectors 78 includes a passage 78A that
receives fuel from the secondary fuel line 82 (FIG. 2), and ejects
a secondary (or second) fuel stream S2 from an outlet 78B. In the
illustrated example, one or more of the outlets 78B of the
secondary plain-jet fuel injectors 78 is forward of the outlet 76B
of the primary fuel injector 76 with respect to the combustor axis
X, or is otherwise upstream of the outlet 76B with respect to a
general direction of flow through the injector passage 88.
[0054] The swirler body 72 is situated about the nozzle 74 to
define a first passage section 88A and a second passage section 88B
of the injector passage 88. The first passage section 88A extends
from an array of vanes 87 that provide a desired amount of airflow
to the first passage section 88A which can vary during different
operating conditions of the engine. The outer wall 90 of the
swirler body 72 is contoured such that the first passage section
88A is the shape of an inward sloping annulus that extends about
the nozzle body 74A and merges into the second passage section 88B.
The contoured, dome-shaped profile of the second end portion 74C of
the nozzle body 74A can reduce a likelihood of low streamwise
velocity in the injector passage 88 upstream of the primary fuel
injector 76, thereby reducing the risk of flame holding,
auto-ignition and flashback.
[0055] The first passage section 88A converges in the aft direction
with respect to the nozzle longitudinal axis N to define a throat
88C. For the purposes of this disclosure, the throat is defined as
the minimum effective cross-sectional area of the injector passage
88 between an outlet 78B of the forwardmost one of the secondary
plain-jet fuel injectors 78 and a passage outlet 88D defined at the
aftmost most portion of the injector passage 88 with respect to the
nozzle longitudinal axis N. The throat 88C is defined at a position
axially forward of, and at a distance from, the passage outlet 88D
and the combustion chamber 62 relative to the nozzle longitudinal
axis N.
[0056] In the illustrated example, the injector passage 88 has a
convergent-divergent profile such that the second passage section
88B diverges along locations aft of the throat 88C, with the
effective cross-sectional area of the injector passage 88
increasing at positions downstream of the throat 88C. In
alternative examples, the injector passage 88 has a
convergent-straight profile such that the second passage section
88B has substantially the same cross-sectional area between the
throat 88C and the passage outlet 88D of the injector passage 88
(depicted by 88B' in FIGS. 4 and 5). The convergent-divergent or
convergent-straight profile narrows the cross sectional area of
passage section 88A, which can significantly increase the air
velocity impacting fuel streams S1 and S2 to improve atomization
quality.
[0057] Each of the secondary plain-jet fuel injectors 78 has a
passage that defines a second fuel injector axis F2 extending
through the outlet 78B. Each of the secondary plain-jet fuel
injectors 78 can be arranged such that a projection of the
respective second fuel injector axis F2 intersects the outer wall
90 of the injector passage 88 along the first passage section 88A.
The secondary fuel injectors 88 are arranged such that the
secondary fuel stream S2 ejected from the outlet 78B is carried by
airflow through the first passage section 88A toward the throat
88C. The entire secondary fuel stream S2 may be carried by airflow
toward the throat 88C without contacting the outer wall 90, or a
portion of the secondary fuel stream S2 may contact the outer wall
90 on its way toward the throat 88C.
[0058] Referring to FIG. 5, a localized region of the outer wall 90
of the first passage section 88A, which intersects the projection
of the second fuel injector axis F2, slopes towards the first fuel
injector axis F1 to define a first passage angle .alpha.. A
localized region of radially inner wall 91 of the nozzle 76
defining the first passage section 88A, which intersects the second
fuel injector axis F2, slopes toward the first fuel injector axis
F1 to define a second passage angle .beta.. The first and/or second
passage angles .alpha., .beta. can be between about 30-50 degrees,
for example. In some examples, the first and/or second passage
angles .alpha., .beta. are between about 40-45 degrees. The second
passage angle .theta. can be within about .+-.5 degrees of the
first passage angle .alpha. such that the radially outer and inner
walls 90, 91 are substantially parallel to each other along a
length of the first passage section 88A.
[0059] The passage angles .alpha., .beta. can be defined such that
the first passage section 88A converges toward the throat 88C,
thereby accelerating a velocity of flow towards the throat 88C. The
increased velocity improves the atomization quality of the fuel
streams S1, S2, including high power conditions. At low power
conditions, the spray droplets from both fuel streams S1, S2 can be
relatively large and vaporization rate can be relatively
insignificant because of relatively low air velocity and
temperature. Furthermore, at low power as much as 100 percent of
the total combustor fuel is injected through the pilot injector
assembly 70, so that most of the fuel from fuel streams S1, S2 is
able to reach the outer wall 90 and form a fuel film on the throat
88C and/or divergent portion of the second passage section 88B to
produce a single surface film. The single surface film is atomized
by air flow from both injector passages 88, 89 and is ignited to
produce a single, relatively high temperature non-premixed pilot
flame to provide improved ignition/relight capability, lean
blowout, and efficiency, for example, during low power operation.
During high power conditions, the velocity or momentum of airflow
through the injector passage 88 can significantly increase, which
can not only significantly improve atomization quality, e.g.,
relatively much smaller droplets, but can also reduce fuel stream
penetration and reduces a likelihood of a surface film being
generated on surfaces of the injector passage 88. In some examples,
for the staged combustor system (FIG. 7) shown for example by
combustor assembly 60 having both main and pilot fuel injector
assemblies 64, 70, less than about 25 percent of total combustor
fuel is injected through the pilot injector assembly 70 during high
power operation such that the fuel stream S2 stays in roughly the
middle of injector passage 88 to help achieve uniform mixing of
fuel and air. Improved atomization plus increased air temperature
at high power can enhance fuel vaporization to improve the degree
of premixing. Improved atomization, optimized fuel penetration and
enhanced fuel vaporization can assist in making fuel stream S2
achieve an improved degree of premixing to form a substantially
premixed flame. Fuel stream S1 is less perfectly mixed with air,
and is ignited to form a stable non-premixed flame during high
power operation. The spray angle of the outlet 76B of the primary
fuel injector 76 can also be defined to maximize the stability of
the non-premixed flame where fuel stream S1 is burned. This stable
non-premixed flame may help to suppress or substantially reduce
possible combustion acoustics.
[0060] A localized region of the radially outer wall 90 along the
second passage section 88B can diverge aft of the throat 88C to
establish a third passage angle .gamma. relative to the first
injector axis F1. The third passage angle .gamma. can be less than
or equal to about 20 degrees, or more narrowly between about 5-15
degrees, for example. For the purposes of this disclosure, the term
"about" means .+-.3 percent of the stated value unless otherwise
disclosed. In some examples, the passage angles .alpha., .beta.
and/or .gamma. are defined with respect to the nozzle longitudinal
axis N. The divergent arrangement of the second passage section 88B
can significantly anchor and assist in stabilizing the pilot flame,
which can assist in reducing or substantially preventing combustion
acoustics.
[0061] Referring to FIG. 6, the first passage section 88A of the
injector passage 88 defines a first passage area A1 with respect to
a first reference plane RF1 swept about the first fuel injector
axis F1 to have substantially annular geometry. The first reference
plane RF1 extends along the second fuel injector axis F2 and
intersects inner and outer walls 90, 91. The second passage section
88B of the injector passage 88 defines a second passage area A2
with respect to a second reference plane RF2 along the throat 88C
that is perpendicular to the first fuel injector axis F1. In some
examples, a ratio of the first passage area A1 to the second
passage area A2 is between about 1.1-2.0, or more narrowly between
about 1.2-1.5, for example, for improving atomization of the
secondary fuel stream S2 ejected by the secondary plain-jet fuel
injectors 78 and for reducing a likelihood of auto-ignition, flame
holding and flashback of the secondary fuel stream S2 in the first
passage section 88A. In some examples, the first and/or second
reference planes RF1, RF2 are defined with respect to the nozzle
longitudinal axis N.
[0062] The relative positions of the outlets 76B, 78B of the fuel
injector 76 and plain-jet fuel injectors 78 can be arranged
relative to each other and/or the throat 88C to provide a desired
amount of premixing of fuel and air in the injector passage 88. For
example, a third reference plane RF3 extends perpendicular from the
first fuel injector axis F1 and intersects the first reference
plane RF1 at the outlet 78B of the forwardmost one of the secondary
plain-jet fuel injectors 78. The throat 88C and a projection of the
outlet 78B of the forwardmost one of the secondary plain-jet fuel
injectors 78 along the third reference plane RF3 define a first
distance D1 with respect to the first fuel injector axis F1. The
outlet 78B of the primary fuel injector 76 and the throat 88C
define a second distance D2 with respect to the first fuel injector
axis F1. A ratio of the first distance D1 to the second distance D2
can be between about 1.5-4.5, or more narrowly between about
2.0-4.0, for example, to reduce a likelihood of auto-ignition of
the secondary fuel stream S2 in the first passage section 88A. In
some examples, the first and/or second distances D1, D2 are defined
with respect to the nozzle longitudinal axis N.
[0063] In some examples, the controller CTRL is operable to
independently meter flow of fuel through the primary and secondary
fuel lines 80, 82. For example, the controller CTRL is operable to
meter flow of fuel through the primary and secondary fuel lines 80,
82 in a first mode, and is operable in a second, different mode,
such that a flow rate through each of the fuel lines 80, 82 differs
from the first mode. In other examples, a fuel split between
primary and secondary fuel lines 80, 82 is pre-determined for
delivering fuel to the pilot fuel injector 70 as a function of
power conditions that can be established in order to reduce the
complexity of the controller CTRL. The fuel split can be linked to
(or dependent upon) the total fuel flow or pressure through the
pilot fuel injector assembly 70 to provide passive control. Fuel
flow through the primary fuel line 80 can be about 50 percent of
the total fuel flow to the pilot fuel injector assembly 70 during
low power operation, for example. In one example, the fuel flow
through the primary fuel line 80 is about 35 percent of the total
fuel flow to the pilot injector assembly 70 during high power
operation.
[0064] FIG. 7 illustrates a process for operating a combustor
assembly in a flowchart 92, such as the combustor assembly 60 of
FIGS. 2-6. At block 93, airflow is accelerated in injector passage
88 from the first passage section 88A toward throat 88C. At block
94A, during a first (or non-staged) mode for low power operation,
substantially all or 100 percent of total fuel is injected through
the pilot injector. The fuel streams S1, S2 are injected into the
injector passages 88A, 88B to establish a relatively stable high
temperature single non-premixed flame. At block 94B, during a
second (or staged) mode, a lesser percentage (e.g., 25 percent) of
the total fuel injected through the pilot injector assembly 70. The
fuel stream S1 is injected by the primary fuel injector 76 into the
second passage section 88B to establish a non-premixed flame, and
fuel stream(s) S2 are injected by secondary plain-jet fuel
injector(s) 78 into the first injector passage 88A to establish a
premixed flame. The remainder of the fuel is injected through the
main fuel injector assembly 64, generally downstream of the pilot
fuel injector assembly 70, to form a relatively large premixed main
flame. In some examples, the first mode corresponds to idle,
initial acceleration, approach and flight idle, and the second mode
corresponds to late acceleration, takeoff, climb and cruise
operating condition of the engine 20.
[0065] In examples, a rate of flow of fuel to the primary fuel
injector 76 and the secondary plain-jet fuel injector(s) 78 and/or
airflow through the injector passage 88 during the first mode or
operating condition differs from the second mode or operating
condition. In other examples, fuel flow through each of the
pre-mixed and non-premixed fuel streams and/or airflow through the
injector passage 88 during the first mode differs from the second
mode. For example, during the second (e.g., high power) mode, less
than about 15 percent of the total fuel is delivered to primary
fuel injector 76 of the pilot fuel injector assembly 70 to form a
stable non-premixed pilot flame and about 85 percent or greater of
the total fuel is delivered to the secondary plain-jet fuel
injectors 78 of pilot fuel injector assembly 70 to form a premixed
main flame having reduced NOx and smoke emissions. At block 95, the
products of combustion from the injector passage 88 are
communicated to downstream portions of the combustion chamber 62
during each of the first and second modes, which is then delivered
downstream to turbine section 28. In some examples, at block 96
fuel from the main fuel injector assembly 64 is injected into the
combustion chamber 62 at a location downstream of the injector
passage 88 to establish a main flame during the second mode, but
not the first mode. About 60-85 percent of the total fuel is
delivered to the main fuel injector assembly 64 and about 15-40
percent is delivered to the pilot fuel injector assembly 70 during
the second mode, and about 100 percent of the total fuel is
delivered to the pilot fuel injector assembly 70 during the first
mode, for example. In one example, about 75 percent of the fuel is
delivered to the main fuel injector assembly 64, and about 25
percent of fuel is delivered to the pilot fuel injector assembly 70
during the second mode.
[0066] Generation of a pilot flame including portions formed by
premixed and non-premixed flames can reduce NOx and smoke emissions
during high power conditions of the engine 20. This decrease in NOx
and smoke emissions relates to a geometry of the injector passage
88 and/or a relative fuel split of the primary fuel injector 76 and
plain-jet fuel injectors 78. This decrease in NOx and smoke
emissions is also based on relatively more uniform and increased
mixing of the fuel and air to produce a relatively leaner uniform
fuel/air mixture, as compared to generation of a non-premixed flame
alone. Generation of a single, combined non-premixed flame provides
a relatively stable pilot flame during low power conditions of the
engine 20.
[0067] An example geometry of a premixed flame PF and a
non-premixed flame NP during high power conditions is illustrated
by FIG. 8. During high power conditions of the engine 20, the
premixed flame PF has a generally annular, outward sloping profile
that extends about the diffusion flame DF having a generally
conical profile. The divergent profile of the second passage
section 88B of the injector passage 88 causes portions of the
non-premixed flame NP to be situated axially forward of the passage
outlet 88D of the injector passage 88 (i.e., approaches a
stoichiometric point of 1.0), which can increase stability of the
non-premixed flame NP. During a low power condition of the engine
20, a single non-premixed flame NP' extends relative further
aftward into the combustion chamber 62, which can be utilized to
ignite fuel injected by the main fuel injector assembly 64 when
transitioning to a high power condition of the engine 20. The
relatively lower amount of soot produced during high power
conditions can be substantially consumed mainly by the large main
flame prior to exiting the combustion chamber 62, thereby further
reducing smoke emission.
[0068] One or more embodiments have been described. Nevertheless,
it will be understood that various modifications may be made. For
example, when reengineering from a baseline engine configuration,
details of the baseline may influence details of any particular
implementation. Accordingly, other embodiments are within the scope
of the following claims.
* * * * *